assert(t.typ != nil)
		if !f(t) {
			return false
		}
	}
	return true
}

// underIs calls f with the underlying types of the specific type terms
// of s and reports whether all calls to f returned true. If there are
// no specific terms, underIs returns the result of f(nil).
func (s *_TypeSet) underIs(f func(Type) bool) bool {
	if !s.hasTerms() {
		return f(nil)
	}
	for _, t := range s.terms {

		assert(t.typ != nil)
		if !f(t) {
			return false
		}
	}
	return true
}

// underIs calls f with the underlying types of the specific type terms
// of s and reports whether all calls to f returned true. If there are
// no specific terms, underIs returns the result of f(nil).
func (s *_TypeSet) underIs(f func(Type) bool) bool {
	if !s.hasTerms() {
		return f(nil)
	}
	for _, t := range s.terms {

		case *Slice, *Chan:
			mode = value

		case *Map:
			if id == _Len {
				mode = value
			}

		case *Interface:
			if !isTypeParam(x.typ) {
				break
			}
			if t.typeSet().underIs(func(t Type) bool {
				switch t := arrayPtrDeref(t).(type) {
				case *Basic:
					if isString(t) && id == _Len {
						return true
					}
				case *Array, *Slice, *Chan:
					return true
				case *Map:

		case *Slice, *Chan:
			mode = value

		case *Map:
			if id == _Len {
				mode = value
			}

		case *Interface:
			if !isTypeParam(x.typ) {
				break
			}
			if t.typeSet().underIs(func(t Type) bool {
				switch t := arrayPtrDeref(t).(type) {
				case *Basic:
					if isString(t) && id == _Len {
						return true
					}
				case *Array, *Slice, *Chan:
					return true
				case *Map:

}

// hasNil reports whether type t includes the nil value.
func hasNil(t Type) bool {
	switch u := under(t).(type) {
	case *Basic:
		return u.kind == UnsafePointer
	case *Slice, *Pointer, *Signature, *Map, *Chan:
		return true
	case *Interface:
		return !isTypeParam(t) || u.typeSet().underIs(func(u Type) bool {
			return u != nil && hasNil(u)
		})
	}
	return false
}

}

// hasNil reports whether type t includes the nil value.
func hasNil(t Type) bool {
	switch u := under(t).(type) {
	case *Basic:
		return u.kind == UnsafePointer
	case *Slice, *Pointer, *Signature, *Map, *Chan:
		return true
	case *Interface:
		return !isTypeParam(t) || u.typeSet().underIs(func(u Type) bool {
			return u != nil && hasNil(u)
		})
	}
	return false
}

		var key, elem Type // key != nil: we must have all maps
		mode := variable   // non-maps result mode
		// TODO(gri) factor out closure and use it for non-typeparam cases as well
		if typ.typeSet().underIs(func(u Type) bool {
			l := int64(-1) // valid if >= 0
			var k, e Type  // k is only set for maps
			switch t := u.(type) {
			case *Basic:
				if isString(t) {
					e = universeByte
					mode = value

		var key, elem Type // key != nil: we must have all maps
		mode := variable   // non-maps result mode
		// TODO(gri) factor out closure and use it for non-typeparam cases as well
		if typ.typeSet().underIs(func(u Type) bool {
			l := int64(-1) // valid if >= 0
			var k, e Type  // k is only set for maps
			switch t := u.(type) {
			case *Basic:
				if isString(t) {
					e = universeByte
					mode = value

     b. You may distribute such Executable Form under the terms of this License,
        or sublicense it under different terms, provided that the license for
        the Executable Form does not attempt to limit or alter the recipients’
        rights in the Source Code Form under this License.

3.3. Distribution of a Larger Work

     You may create and distribute a Larger Work under terms of Your choice,

     b. You may distribute such Executable Form under the terms of this License,
        or sublicense it under different terms, provided that the license for
        the Executable Form does not attempt to limit or alter the recipients’
        rights in the Source Code Form under this License.

3.3. Distribution of a Larger Work

     You may create and distribute a Larger Work under terms of Your choice,